Patent application title: Electrical hand-held power tool

Abstract:

An electrical hand-held power tool includes an outer housing (12) in which
there are located a percussion mechanism (18), a motor (16) for driving
the percussion mechanism (18), a gear unit (17) for connecting the motor
(16) with the percussion mechanism (18), a control electronics (19) for
controlling operation of the power tool (11), and a closed cooling
circuit (21) for cooling medium for cooling above-listed components of
the power tool (11). A heat exchanger (26), which is fixedly connected
with the power tool (11), is arranged in the cooling circuit (21) for
cooling the cooling medium.

Claims:

1. An electrical hand-held power tool, comprising an outer housing (12); a
percussion mechanism (18) located in the outer housing (12); a motor (16)
located in the housing (12) for driving the percussion mechanism (18); a
gear unit (17) for connecting the motor (16) with the percussion
mechanism (18); a control electronics (19) likewise located in the
housing (12) for controlling operation of the power tool (11); a closed
cooling circuit (21) arranged in the outer housing (12) for cooling
medium for cooling above-listed components of the power tool (11); and a
heat exchanger (26) arranged in the cooling circuit (21) for cooling the
cooling medium and fixedly connected with the power tool (11).

2. An electrical hand-held power tool according to claim 1 wherein the
heat exchanger (26) is arranged in the cooling circuit (21) upstream of
the control electronics (19) in a flow direction of the cooling medium.

3. An electrical hand-held power tool according to claim 1, wherein the
heat exchanger (26) is arranged on the outer housing (12).

4. An electrical hand-held power tool according to claim 1, further
comprising a pressure-generating pump (31) for the cooling medium
arranged in the cooling circuit (21) downstream of the heat exchanger in
a flow direction of the cooling medium.

5. An electrical hand-held power tool according to claim 1, further
comprising a bypass (24) provided in the cooling circuit for bypassing
the heat exchanger (26).

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an electrical hand-held power tool
including an outer housing in which there are arranged a percussion
mechanism, a motor for driving the percussion mechanism, a gear unit for
connecting the motor with the percussion mechanism, a control electronics
for controlling operation of the power tool, and a closed cooling circuit
for cooling medium for cooling above-listed components of the power tool.

[0003]2. Description of the Prior Art

[0004]In electrical hand-held power tools with a percussion mechanism such
as hammer drill, combination or chisel hammer, the mechanical energy,
which is produced by the motor, is converted by the gear unit and the
percussion mechanism in a rotary and/or percussion movement of a working
tool received in the power tool.

[0005]In order to remove the generated heat, electrical hand-held power
tools with a forced aeration are used. In these power tools, a cooling
outside air is propelled by a ventilator through the power tool. The
drawback of this solution consists in that the these power tools do not
provide any protection with regard to moisture that would conform to the
requirements of International Standard as defined by a respective IPX
Code, or would provide such protection only with large constructive
expenditures. IPX Code (IP stands for "International Protection" which
sometimes is interpreted as "Ingress Protection") classifies the level of
protection of instruments and equipment inside an enclosure against
harmful ingress of water. E.g., IPX4 indicates protection against
splashing water, IPX5 indicates protection against water jets. E.i., in
both cases, no harmful effect on the operation of an instrument or
equipment occurs. Thus, IPX Code indicates the suitability of an
instrument of equipment, of a power tool in the present case, for
different environmental conditions.

[0006]German Patent Publication DE 100 37 418 A1 discloses an electrical
hand-held power tool including an outer housing in which there are
arranged a percussion mechanism, a motor for driving the percussion
mechanism, a gear unit for connecting the motor with the percussion
mechanism, a control electronics for controlling operation of the power
tool, and a closed cooling circuit for cooling medium for cooling the
above-listed components of the power tool. With a closed cooling circuit,
an electrical hand-held power tool can be completely sealed outwardly
and, thereby insures type of protection defined by the code IPX4 and
higher without particularly large expenses.

[0007]The drawback of the power tool disclosed in DE 100 37 418 A1
consists in that the cooling medium cannot satisfactorily release the
absorbed heat into environment after a long-lasting operation and,
thereby heats up. Therefore, the operation of the power tool should be
stopped until an adequately low temperature level of the cooling medium
is reached.

[0008]Accordingly, an object of the present invention is to provide an
electrical hand-held power tool with a closed cooling circuit for cooling
power tool components and which insures type of protection defined by
Code IPX4 and higher and enables a lasting operation of the power tool
for a long period of time.

SUMMARY OF THE INVENTION

[0009]This and other objects of the present invention, which will become
apparent hereinafter, are achieved by providing in the cooling circuit a
heat exchanger fixedly connected with the power tool. The heat exchanger
extracts the heat from the heated cooling medium that absorbed it from
the power tool components, and insures an adequately low temperature
level of the cooling medium for cooling the power tool components.
Advantageously, liquid cooling medium is used, e.g., water. The power
tool with a closed cooling circuit that includes a heat exchanger, can
operate for a much longer period of time than known percussion electrical
hand-held power tools.

[0010]In this connection, under a heat exchanger is understood an
apparatus that increases the surface between a cooling medium, e.g.,
liquid cooling medium, such as water, and another medium, e.g., a gaseous
medium, such as air. Advantageously, the heat exchanger is formed of a
material having a good heat conductance and a large surface. The heat
exchanger has, e.g., tubes or hollow plates formed of metal and which
reciprocate in a limited space, and through which the cooling medium
flows. Thereby, a larger surface is provided for transfer of heat to the
other medium than with a pure liquid through-flow, as disclosed in DE 100
37 418 A. Such heat exchangers are called heat transmitters. The heat
exchange is effected by a free convection. Alternatively, the heat
exchange can be effected by a forced convection, e.g., with a fan mounted
on the heat exchanger.

[0011]With a closed cooling circuit arranged in the outer housing and with
a heat exchanger fixedly connected with the power tool, a complete
encapsulation of the components of the electrical hand-held power tool
becomes possible, in addition to insuring an adequate cooling of the
power tool components. The requirements for type of protection, which is
defined by code IPX4 and higher, are met with a simple construction of
the electrical hand-held power tool. The user can use the inventive
electrical hand-held power tool during rain in an open-air environment or
under humid environmental conditions. In addition, the inventive
electrical hand-held power tool can be used all-round, without hindrance
that may be caused by elements projecting from the power tool. This is
because the inventive electrical hand-held power tool, while insuring an
adequate cooling of power tool components, does not require any external
cooling apparatus or an external connection for the cooling medium.

[0012]Advantageously, the heat exchanger is arranged in the cooing circuit
upstream of the control electronics in a flow direction of the cooling
medium. This insures an advantageous cooling of the control electronics.
This is because the cooling medium, which was cooled by the heat
exchanger, is not heated again by another heat-releasing component of the
power tool. Thereby, a strong protection of electronic components from
overheating is insured even at a lasting operation of the power tool for
a very long period of time.

[0013]Preferably, the heat exchanger is arranged on the outer housing of
the power tool for a direct heat exchange with the surrounding air. This
insures an advantageous heat transmission from the cooling medium to the
air that surrounds the power tool, and provides for a simple construction
of the power tool.

[0014]In an advantageous embodiment of the present invention, the heat
exchanger is mounted on the outer side of the outer housing for a better
heat transmission. The conduits of the cooling circuit extend through the
outer housing with the leadthroughs being preferably sealed.

[0015]Advantageously, a pressure-generating pump for the cooling medium is
arranged in the cooling circuit downstream of the heat exchanger in a
flow direction of the cooling medium. The cooling medium is constantly
pumped through the heat exchanger, and the cooling medium is brought to a
low level for an adequate cooling of the power tool components.
Advantageously, the pump is located between the control electronics and
the motor and is mechanically connected with the motor for being driven
thereby.

[0016]Advantageously, a bypass is provided in cooling circuit for
bypassing the heat exchanger. The bypass is advantageously
temperature-controlled for bypassing the heat exchanger.

[0017]At low environmental temperatures, an optimal operational
temperature of the power tool is rapidly achieved. As soon as the
operational temperature is achieved, the cooling medium is again passed
through the heat exchanger for an adequate cooling of the power tool
components. Advantageously, dependent on the type of the control used,
correspondingly formed valves are provided at the ends of the bypass.

[0018]The novel features of the present invention, which are considered as
characteristic for the invention, are set forth in the appended claims.
The invention itself, however, both as to its construction and its mode
of operation, together with additional advantages and objects thereof,
will be best understood from the following detailed description of
preferred embodiment, when read with reference to the accompanying
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]In the drawings:

[0020]Single FIGURE shows a schematic side view of an electrical hand-held
power tool according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021]A liquid-cooled electrical hand-held power tool 11 according to the
present invention, which is shown in the drawing, has an outer housing 12
with a handle 13. In the outer housing 12, there are arranged a motor 16,
a gear unit 17, a percussion mechanism 18, and control electronics 19. A
closed cooling circuit 21 is completely arranged in the outer housing 12
for cooling the above-listed components of the power tool 12. The cooling
circuit 21 includes a heat exchanger 26 for cooling a liquid cooling
medium. The heat exchanger 26 communicates with the environment and, to
this end, is arranged directly on the housing 12.

[0022]The heat exchanger 26 is located in the cooling circuit 21 upstream
of the control electronics 19 in the direction of flow of the cooling
medium. In order to insure an adequate flow velocity of the cooling
medium in the cooling circuit 21, there is provided a pressure-generating
pump 31 which is arranged in the cooling circuit 21 downstream, in the
cooling medium flow direction, of the heat exchanger 26. In the drawing,
the flow direction of the cooling medium is shown with arrows 22 and 23.

[0023]Further, there is provided, in the cooling circuit 21, a bypass 24
for bypassing the heat exchanger 26. Through the bypass 24, the cooling
medium can be guided around the heat exchanger 26 until an optimal
operational temperature of the electrical power tool is reached.

[0024]Though the present invention was shown and described with references
to the preferred embodiment, such is merely illustrative of the present
invention and is not to be construed as a limitation thereof and various
modifications of the present invention will be apparent to those skilled
in the art. It is therefore not intended that the present invention be
limited to the disclosed embodiment or details thereof, and the present
invention includes all variations and/or alternative embodiments within
the spirit and scope of the present invention as defined by the appended
claims.